Niall Ó Glacáin,^[5] sometimes anglicised as Nial O'Glacan^[6][1] (c. 1563 – 1653) was an Irish physician and plague doctor who worked to treat victims of bubonic plague outbreaks throughout continental Europe. He was a physician to Hugh Roe O'Donnell and King Louis XIII.

Working as a physician to the prominent O'Donnell clan during the Irish Nine Years' War, he may have followed them to Spain after the Siege of Kinsale, where he spent two decades practicing medicine.

He moved to France in the 1620s, settling in Toulouse to publish his work Tractatus de Peste, a treatise on plague treatment. Later in life he took up a post at the University of Bologna as Professor of Medicine.

Ó Glacáin was a pioneer in pathological anatomy, with his work predating that of anatomist Giovanni Battista Morgagni by several decades.^[7][1]

Ó Glacáin was born in Tyrconnell in the latter half of the sixteenth century.^[7][1][2] Some historians give him a birth date of around 1563, owing to a 1653 engraving that gives his age as 90.^[4][8] Professor Giorgio Scharpes estimated Ó Glacáin to be about 48 when recommending him to the University of Bologna in the 1630s, which would mean he was born in the 1580s.^[4]

Ó Glacáin's medical education was founded on the works of Greek physicians Galen and Hippocrates, whom he refers to in his later works.^[1][3][4] He probably received his early education from the local Donlevy family, a hereditary family of physicians.^[1][9][7] At the time, most medical families were attached to a powerful clan – the Donlevys were the personal physicians of Tyrconnell's ruling O'Donnell clan.^[9] Conversely, Charles Cameron suggests Ó Glacáin received his medical education abroad.^[2]

Owen Ultach MacDonlevy – the last recorded ollam leighis (official physician) of the O'Donnells – died in 1586.^[10] By the early 1600s, Ó Glacáin was working as the O'Donnell's physician.^[1]

After the Irish defeat at the Battle of Kinsale, the O'Donnell clan left Ireland to seek refuge in Spain.^[11] Ó Glacáin treated clan chief Hugh Roe O'Donnell for a bubonic plague sore during his illness and eventual death at the Spanish court in 1602.^[9][1][7] Ó Glacáin writes in his work Tractatus de Peste:

"...I was staying with my Magnanimous Hugh O'Donnell the Great Prince of Tír Chonaill in the court of the King of Spain, with a venereal bubo. Some of the citizens of Madrid, who would not readily accept the treatment of any of the surgeons, approached me, and quickly and successfully recovered unharmed with the following poultice..."^[3]

Ó Glacáin subsequently spent many years practicing medicine in Salamanca. In 1622, he moved to Valencia, residing there for two years.^[7][1][5] He mentions "Dyonisius Ultanus", of the Donlevy family, as a patient he treated in Valencia.^[3]

In 1621, Ó Glacáin was recorded as attending the Irish College in Bordeaux under Archbishop François d'Escoubleau de Sourdis.^[6]

In July 1625, he graduated from the University of Cahors [en] in Southern France. It would later merge with the University of Toulouse in 1751. It is also possible Ó Glacáin attended the Irish College in Toulouse, Bordeaux's sister school.^[12][13]

Around 1628, he worked as a travelling plague doctor, treating victims at local hospitals in towns such as Fons, Figeac, Capdenac, Cajarc, Rouergue and Floyeac.^[1][14] His work was encouraged by the Bishop of Cahors.^[14]

He had settled in Toulouse in time to treat victims of the plague outbreak of 1628.^[5] MacCuinneagáin states that Ó Glacáin "gained high esteem and general consideration because of the devotion which he showed in braving the contagion to succor the sick. He was appointed physician at the xenodochium pestiferorum, the plague hospital at Toulouse in 1628 and was appointed to the University there with the title Premier Professor of Medicine."^[4]

Ó Glacáin also spent time in Paris as both physician and Privy Councillor to King Louis XIII.^[9][7][1]

By now a respected authority on plague treatment,^[2] Ó Glacáin published his most famous work, Tractatus de Peste, Seu Brevis, Facilis et Experta Methodus Curandi Pestem ('A Treatise on Plague, or A Short, Easy, and Expert Method for the Curing of Plague'), at Toulouse in May 1629.^[14][2][1] It contained his concise descriptions of the plague, its various effects on different patients such as buboes, rashes, headaches, vomiting, and coma. Suggested treatments including bleeding, the use of clysters, purgatives, and fumigation.^[3][1]

An especially interesting part of the text is a description of four post-mortems which he carried out, where he noted the occurrence of petechial haemorrhages which "covered the surface of the victims' lungs and also the swelling of the spleen."^[4]

Ó Glacáin also references the protective clothing worn by plague doctors, including leather coats, gauntlets and long beak-like masks filled with fumigants.^[4]

Ó Glacáin moved to Italy in the early 1630s. He was "head-hunted" by the Faculty of Medicine at the University of Bologna, which had a tradition of employing very eminent foreign doctors as their Medicina Sopraordinaria (Professor of Medicine). To this end, the university's senate asked Giorgio Scharpes (Professor of Medicine, 1634–1637) to write a report on Ó Glacáin, whose fame by then spanned all of Europe. Scharpes' reply was as follows:

With regard to religion Mr. Glacáin is a Catholic, and there is no doubt because it would be difficult for a heretic to live in a city like Tolosa (Toulouse) which is known to be one of the most Catholic places and where they cannot bear heretics. Mr. Glacáin is about 48. He is famous because during the plague in these regions of France during the years 1627 to 1629 he was very helpful and in the year 1629 he produced a book whose title is Tractatus de Peste ... and I invite you to read this book to understand exactly why Mr. Glacáin is valuable and why he is still teaching in the University of Tolosa ... About his teaching he is well estimated because he is a good philosopher, good in fighting against his enemies that accused him of being a magician; his book can confirm that he was not a magician ... Mr. Glacáin knows Greek very well ... talking about the other questions ... from a letter from Mr. Glacáin where he says he would really like to serve the University of Bologna, I can understand that there will not be any problem for the salary and for him to come."^[4]

In 1646, he became Professor of Medicine at the University of Bologna.^[1][7][8] MacCuinneagáin gives this date as 1642, and claims Ó Glacáin held this office until his death.^[4]

During his years in Bologna, Ó Glacáin wrote his final work, Cursus Medicus ('A Physician's Course'), which was published in three volumes in 1655.^[1][9][2] The first volume dealt with physiology, the second pathology,^[1][4] and the third – published after his death – on the theory of signs. This final volume dealt with the different diagnosis by doctors, descriptions of diseases, and was overall an introduction to the modern concept of differential diagnosis.^[4] Two other Irish residents in the city, Gregory Fallon of Connacht and the Jesuit Phillip Roche, wrote commendatory verses prefixing volume two.^[14][4]

Although the details of Ó Glacáin's personal life are almost unknown,^[7][4] many of his associates are referenced in contemporary records. He entertained Bishop of Ferns Nicholas French and Sir Nicholas Plunkett at his home in Bologna, when the latter were on their way to Rome in 1648. In collaboration with them, he wrote eulogistic poems in Latin to Pope Innocent X, titled Regni Hiberniae ad Sanctissimi Innocenti Pont. Max. Pyramides Encomiasticae.^[1][4] Ó Glacáin himself visited Rome at some point.^[14]

In his later work, he mentions another friend, the Franciscan catechist and grammarian Froinsias Ó Maolmhuaidh.^[14][4] Ó Glacáin was also an associate of Irish bishop Peter Talbot^[1] and Portuguese physician Gabriel da Fonseca, personal physician to Innocent X.^[8] Other friends in Italy include Gerard O'Fearail and John O'Fahy.^[14]

Ó Glacáin died in 1653,^[4][15] probably in Bologna.^[16] The final volume of Cursus Medicus begins with his eulogy, as written by Peter von Adrian Brocke, Professor of Eloquence at Lucca:

With healing art he arms us to repel, dire troops of agues and of fevers fell, whatever ills the patient may endure, known or unknown, unerring is his cure..."^[5][17][15]

• Tractatus de Peste, Seu Brevis, Facilis et Experta Methodud Curandi Pestem, University of Toulouse Press, 1629.
• Cursus Medicus, libris tredecem propositus, Vol 1, Vol 2, Vol 3, University of Bologna press, 1655.